The U.S. Pat. No. 5,702,447 A discloses a glenoid prosthesis having a planar metal socket for threading into a shoulder-blade bone. The metal socket is fitted on its inner side with a rib. A pan-like plastic socket part can be partly inserted in an oblique position under the rib, and then securely joined with the metal socket by pushing it down. The exact positioning of the plastic socket part in the metal socket demands a high precision. Any substance between the plastic socket part and the metal socket, such as for instance blood or tissue portions, may hinder a completion of the connection. Thanks to a simple tilting motion, the plastic socket part can be released from the metal socket, and the prosthesis is no longer operable. The two components of the prosthesis, the plastic socket part and the metal socket, are then totally detached from each other and cannot be securely recombined by a simple operation.
The patent application US 2004/0064189 A1 disclosed a glenoid element with an anchoring part to be anchored in a bone by a screw, and a socket part connected to the anchoring part by a snap-in device set in its bottom. When assembling the socket part with the anchoring part, however, the socket part may cant or tilt over in the anchoring part, thus impeding a secure connection of the two parts, and demanding a high precision. Moreover, any portions of tissue and blood eventually lodging between the socket part and the anchoring part aggravate a secure connection.